1. Field of the Invention
The present invention relates to a combination type thin film magnetic head constructed by stacking an inductive type writing thin film magnetic head and a magnetoresistive type reading thin film magnetic head on a surface of a substrate in an electrically insulating and magnetically isolated manner. The present invention also relates to a method of manufacturing such a thin film magnetic head.
2. Description of the Related Art
Recently a surface recording density of a hard disc device has been improved, and it has been required to develop a thin film magnetic head having an improved performance accordingly. A combination type thin film magnetic head is constructed by stacking an inductive type thin film magnetic head intended for writing and a magnetoresistive type thin film magnetic head intended for reading on a substrate, and has been practically used. In general, as a reading magnetoresistive element, an element utilizing anisotropic magnetoresistive (AMR) effect has been used so far, but there has been further developed a GMR reproducing element utilizing a giant magnetoresistive (GMR) effect having a resistance change ratio higher than that of the normal anisotropic magnetoresistive effect by several times.
In the present specification, elements exhibiting a magnetoresistive effect such as AMR and GMR reproducing elements are termed as a magnetoresistive reproducing element or MR reproducing element.
By using the AMR reproducing element, a very high surface recording density of several gigabits/inch.sup.2 has been realized, and a surface recording density can be further increased by using the GMR element. By increasing a surface recording density in this manner, it is possible to realize a hard disc device which has a very large storage capacity of more than 10 gigabytes.
A height of a magnetoresistive reproducing element (MR Height: MRH) is one of factors which determine a performance of a reproducing head including a magnetoresistive reproducing element. The MR height MRH is a distance measured from an air bearing surface on which one edge of the magnetoresistive reproducing element is exposed to the other edge of the element remote from the air bearing surface. During a manufacturing process of the magnetic head, a desired MR height MRH can be obtained by controlling an amount of polishing the air bearing surface.
At the same time, the performance of the recording magnetic head is also required to be improved in accordance with the improvement of the performance of the reproducing magnetic head. In order to increase a surface recording density, it is necessary to make a track density on a magnetic record medium as high as possible. For this purpose, a width of a write gap at the air bearing surface has to be reduced to a value within a range from several micron meters to several sub-micron meters. In order to satisfy such a requirement, the semiconductor manufacturing process has been adopted for manufacturing the thin film magnetic head.
One of factors determining the performance of the inductive type writing thin film magnetic head is a throat height TH. This throat height TH is a distance of a pole portion measured from the air bearing surface to an edge of an insulating layer which serves to separate a thin film coil from the air bearing surface. It has been required to shorten this distance as small as possible. The reduction of this throat height is also decided by an amount of polishing the air bearing surface.
Therefore, in order to improve the performance of the combination type thin film magnetic head including the inductive type recording head and magnetoresistive reading head, it is very important to make the performance of the recording head and the performance of the reading head to be balanced with each other, rather than to improve the performances of these heads independently.
FIGS. 1-12 show successive steps of a method of manufacturing a conventional standard thin film magnetic head and a finally manufactured completed thin film magnetic head. It should be noted that the thin film magnetic head is of a combination type in which the inductive type thin film magnetic head for writing is stacked on the reproducing MR element.
First of all, as shown in FIG. 1, an alumina insulating layer 12 having a thickness of about 5-10 .mu.m is deposited on a substance 11 made of, for instance AlTiC.
Next, as shown in FIG. 2, a bottom shield magnetic layer 13 which protects the MR reproduction element of the reproducing head from the influence of an external magnetic field, is formed with a thickness of 3 .mu.m. Then, as shown in FIG. 3, an alumina insulating layer 14 of thickness 100-150 nm serving as a bottom shield gap layer is formed by sputtering alumina.
As illustrated in FIG. 3, a magnetoresistive layer (MR layer) 15 made of a material having the magnetoresistive effect and constituting the MR reproduction element is formed on the shield gap layer 114 with a thickness of several tens nano meters and is then shaped into a given pattern by the highly precise mask alignment.
Then, as shown in the FIG. 4, an alumina insulating layer 16 serving as a top shielding layer like as the alumina insulating layer 14 is formed such that the magnetoresistive layer 15 is embedded within the insulating layers 14 and 16.
Next, as shown in the FIG. 5, a magnetic layer 17 made of a permalloy is formed with a thickness of 3-4 .mu.m. This magnetic layer 17 has not only the function of the upper shield layer which magnetically shields the MR reproduction element together with the above described bottom shield layer 13, but also has the function of one of poles of the writing thin film magnetic head. Here, the magnetic layer 17 is called a first magnetic layer by taking into account the latter function.
Then, as depicted in FIG. 6, a write gap layer 18 made of a non-magnetic material such as alumina and having a thickness of about 150-300 nm is formed on the first magnetic layer 17, and an electrically insulating layer 19 made of a photoresist is formed on the write gap layer into a given pattern by the mask alignment of high precision. Further, a first layer thin film coil 20 made of, for instance a copper is formed on the photoresist layer 19.
Continuously, as shown in FIG. 7, after forming an electrically insulating photoresist layer 21 on the thin film coil 20 by the highly precise mask alignment, the photoresist layer is sintered at a temperature of, for example 250.degree. C.
In addition, as shown in FIG. 8, a second layer thin film coil 22 is formed on the flattened surface of the photoresist layer 21. Next, after forming a photoresist layer 23 on the second layer thin film coil 22 with the highly precise mask alignment, the photoresist layer is flattened by baking it at a temperature of, for example 250.degree. C.
As described above, the reason why the photoresist layers 19, 21 and 23 are formed by the highly precise mask alignment process, is that the throat height TH and MR height MRH are defined with reference to a position of the edges of the photoresist layers.
Next, as shown in FIG. 9, a second magnetic layer 24 made of, for example a permalloy and having a thickness of 3-4 .mu.m is selectively formed on the gap layer and photoresist layers 19, 21 and 23 in accordance with a desired pattern. This second magnetic layer 124 is coupled with the first magnetic layer 17 at a rear position remote from the magnetoresistive layer 15, and the thin film coil 20, 22 passes through a closed magnetic circuit composed of the first and second magnetic layers. The second magnetic layer 24 includes a pole portion having desired size and shape for defining a track width W.
Furthermore, an overcoat layer 25 made of alumina is deposited on the exposed surface of the write gap layer 18 and second magnetic layer 24. In an actual thin film magnetic head, electric conductors and contact pads for performing the electrical connection to the thin film coils 20, 22 and MR reproduction element are formed, but they are not shown in the drawings.
In an actual manufacturing process, the above mentioned substrate 11 is formed by a wafer, and after forming a number of thin film magnetic head units in the wafer in matrix, the wafer is divided into a plurality of bars, in each of which a plurality of thin film magnetic head units are aligned, and finally the bar is divided into respective thin film magnetic heads.
That is to say, as shown in FIG. 9, a side surface 26 of the substrate 11 on which the magnetoresistive layer 15 is exposed is polished to form an air bearing surface 27 which is opposed to a magnetic record medium. During the formation of the air bearing surface 27, the magnetoresistive layer 15 is also polished to form a MR reproducing element 28, and at the same time the throat height TH of the inductive type thin film recording magnetic head and the MR height MRH of the magnetoresistive type reproducing element are determined.
When the air bearing surface 27 is polished, it is difficult to perform the polishing while the throat height and MR height are actually monitored. Therefore, a resistance measuring circuit is connected to the conductive patters (not shown) connected to the magnetoresistive layer 15, a change in resistance which is reduced in accordance with a reduction of the height of the magnetoresistive layer due to the polishing is measured as a change in a current, and an amount of polishing is calculated from the variation in the thus measured current. That is to say, by performing the polishing operation until the resistance value of the MR reproducing element 28 becomes a predetermined value, desired throat height and MR height are attained.
FIGS. 10, 11 and 12 are cross sectional, front and plan views, respectively showing the completed conventional thin film magnetic head, while the overcoat layer 25 is omitted. It should be noted that in FIG. 10, the alumina insulating layers 14 and 16 surrounding the MR reproducing element 28 are shown as a single insulating layer, and in FIG. 12, the thin film coil 20, 22 is shown concentrically for the sake of simplicity.
As clearly shown in FIG. 10, an angle .theta. (apex angle) between a line S connecting side edges of the photoresist layers 19, 21, 23 for isolating the thin film coil 20, 22 and the upper surface of the second magnetic layer 24 is an important factor for determining the performance of the thin film magnetic head together with the above described throat height TH and MR height MRH.
Furthermore, as shown in the plan view of FIG. 12, the width W of a pole portion 24a of the second magnetic layer 24 is small. Since the width of the track recorded on the magnetic record medium is defined by this width W, it is necessary to narrow this width as small as possible in order to achieve a high surface recording density.
In order to improve the surface recording density of the above mentioned combination type thin film magnetic head, it has been proposed to form the MR layer 15 by spin valve GMR film, super lattice GMR film or granular GMR film. Furthermore, in order to make the reproduction sensitivity high, it has been proposed to reduce the MR height.
In accordance with the improvement of the reproducing element, a problem of the thermal asperity has occurred. In the thermal asperity, the reproducing performance of the reproducing element is degraded due to its heat generation. It has been proposed to form the bottom shield layer 13 and shield gap layers 14, 16 of a material having a high cooling faculty. To this end, the lower shield layer 13 is made of a magnetic material such as permalloy and sendust (Si--Al--Fe), and the shield gap layers 14, 16 are made of alumina insulating material. In general, the shield gap layer 14, 16 made of alumina has a thickness of 100-150 nm and is formed by sputtering.
As explained above, in order to solve the problem of the thermal asperity, the thickness of the shield gap layers 14, 16 has to be small such as 50-100 nm. Then, the electrical insulating property and magnetic shielding property between the MR element 28 and the bottom and top shield layers 13 and 17 are liable to be degraded and further the electrically insulating property between the conductive layers 29, 30 and the bottom and top shield layers 13 and 17 due to pin holes and particles contained in the shield gap layers 14, 16. Therefore, the shield gap layers 14, 16 could not be sufficiently thin.
In Japanese Patent Application Laid-open Publication Kokai Hei 6-334237 corresponding to U.S. Pat. No. 5,617,277, in order to improve the electrical insulating property between conductive layers connected to an MR element and shield layers, a thickness of a part of a shield gap layer situating at the MR element is selectively decreased and a back-fill insulating layer is formed on the thus thinned part of the shield gap layer and the conductive layers are formed on the back-fill layer. In such a structure, it is possible to improve the insulating property between the conductive layers and the bottom shield layer. However, a portion of the bottom shield gap situating below the MR element has a very large thickness, and thus the above mentioned problem of the thermal asperity becomes manifest and the reproducing performance becomes worse.
In Japanese Patent Application Laid-open Publication Kokai Hei 9-91632, there is described a combination type thin film magnetic head, in which in order to leakage of a magnetic flux from a inductive type writing magnetic head into a bottom shield of a magnetoresistive type reproducing element, the bottom shield is locally formed exclusively below the MR element and a remaining portion is filled with an insulating layer. In such a structure, since the insulating layer is formed under the conductive layers, the insulating property is not degraded even if the bottom shield gap layer has a small thickness. However, the lower shield layer is existent only under the MR element, the magnetic shielding could not be effected sufficiently and the MR element might be affected by an external magnetic field. In this manner, the reproducing property might be degraded.
Moreover, in the inductive type thin film magnetic head, a width W of the pole portion 24a of the second magnetic layer 23 is one of factors determining the performance of the magnetic head. Particularly, in order to improve the surface recording density, the width W of the pole portion 24a has to be smaller than about 1 .mu.m.
In the known combination type thin film magnetic head, prior to forming the second magnetic layer 24 by a selective plating, a photoresist layer having a thickness of 3-4 .mu.m is formed on the insulating layers 19, 21, 23 having a thickness of 8-10 .mu.m. Then, at a bottom portion of the insulating layers, i.e. on the write gap layer 18, a thickness of the photoresist layer becomes 8-10 .mu.m.
When the pole portion 24a of the second magnetic layer 24 has to be formed to have a width W of about 1 .mu.m, it is necessary to form a pattern of 1 .mu.m in the photoresist layer having a thickness of 8-10 .mu.m. However, such a fine patterning is very difficult and it is almost impossible to make a width W of the pole portion 24a of the second magnetic layer 24 smaller than 1 .mu.m.
In case of forming the second magnetic layer 24 by electroplating, a thin permalloy film has to be formed on a whole surface of the insulating layers 19, 21, 23 by sputtering. Upon exposure in the photolithography, light might be reflected by said thin permalloy film and the pole portion 24a of the second magnetic layer 24 could not be patterned precisely.